Data storage systems, such as disc drives, typically store information on surfaces of storage media such as magnetic or optical discs. In a typical disc drive, a number of discs are mounted together on a spindle to form a disc stack. The spindle causes the discs to spin and the data surfaces of the disc to pass under respective hydrodynamic and aerodynamic bearing disc head sliders. These head sliders are typically mounted on an actuator arm that moves the head sliders in tandem over the disc surfaces such that all of the head sliders are at the same approximate disc radius at the same time.
When information is stored on a disc it is generally stored in a set of concentric data tracks. The tracks on the disc surface are typically divided into data sectors. Data sectors are the basic units of data storage on a disc surface. A sector is a “pie-shaped” angular section of a track that is bounded on two sides by radii of the disc and on the other side by the perimeter of the circle that defines the track. In other words, the sector is a small storage segment along the length of a track.
Most tracks are available for read/write access by the host computer. These tracks contain user data. Generally, defective media, such as discs, are one of the prime sources of error in either temporary or permanent data retrieval. For example, some defective sectors can form at the time of disc manufacture. Other defects, however, can arise in any of the sectors at various times during the lifetime of the storage system (grown defects). Grown defects include, for example, invading foreign particles which become embedded onto the surface of the disc, or external shocks to the storage system which can cause the transducer to nick or crash onto the surface of the disc.
More recently, capacity growth of storage media has outpaced demand. The increased capacity of storage media has pushed data closer and closer together which puts stress on the reliability of data. Although error recovery mechanisms in the disc drive can aid in recovering data from defective portions of the media, error recovery mechanisms can not recover all data that is, located on defective portions of the media.
Embodiments of the present invention provide solutions to these and other problems, and offer other advantages over the prior art.